The manufacture of some asphalt roofing products includes a moving sheet, of fiberglass fabric, paper or composite materials, coated with a mixture of asphalt and filler, then applying colored granular media to the asphalt coated surface as the sheet runs under a transverse curtain of falling granules. The sheet is cooled and cut into asphalt shingles.
Conventional granule dispensing is carried out using a rotating fluted roll that starts and stops thus dispersing granules onto the sheet. An example of a conventional fluted roll granule dispenser is described in United States Patent Publication US 2011/0229636 and need not be described in further detail here.
There is a need for depositing granules in clearly defined patterns, and for controlling the volume of granules to produce uniform layers over their length from the transverse leading edge to the transverse trailing edge.
Using conventional dispensers, a pattern rectangular patches of different color blends contiguous to each other is achieved by dropping different granules using multiple dispensers in a lengthwise consecutive series as the sheet proceeds downstream. Because the start and stop of granule flow from the conventional dispensers is not instantaneous, there are areas produced where there is not a sufficient thickness of granules and these areas are contaminated by the adjacent overlapping layers of other color mixtures. The leading and trailing edges taper in thickness which prevents the production of a clear division between the adjacent rectangular patches of different colors.
Features that distinguish the present invention from the background art will be apparent from review of the disclosure, drawings and description of the invention presented below.